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For a 6502, what is the assembly convention for calling a 16 bit word into the accumulator from memory to increment as a variable? (lemmy.world)

submitted 2 weeks ago by j4k3@lemmy.world to c/asklemmy@lemmy.world

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I figured one of y'all would just know seeing how ubiquitous the 6502 is. I'm not following any tutorial at the moment and it has been too long since I last mucked around in assembly. I have the programming manual but it is convoluted between the 6502 and 65C816 stuff.

I'm messing with the little Easy 6502 emulator (Flatpak/FlatHub). I want to nest a couple of loops. I should probably just use the stack, but I went down this rabbit hole and damn it I want to find the rabbit!

I want something like (crude):

define lineL $1000
define lineH $1001

LDA $00
STA $lineL
LDA $02
STA $lineH

Hopefully I have that endian right... So now I have a 2 byte word starting at address 0×1000 and loaded with 0x0200. I want to increment this value as a 16 bit variable up to 0x05FF. What I am struggling with is which addressing mode indexes like this or if this must be manually implemented (– which does not seem right to me).

I'll figure it out on my own in the next couple of hours regardless. It is more fun to chat and see the spectrum of knowledge here, or maybe not, either way, ya don't know if ya don't try. Skool me Woz

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[–] abbadon420@sh.itjust.works 3 points 2 weeks ago

I watched a whole lot of Ben Eater and Usagi Electrics, but I still can't write any assembly. It's more fun to watch than to do imho.